1. Field of the Invention
The present invention generally relates to a wheel support bearing assembly equipped with a magnetic encoder for detecting the number of revolutions of a vehicle wheel as a component part of an anti-skid brake system or the like. Particularly, the present invention relates to the wheel support bearing assembly of a kind wherein the magnetic encoder is employed as a component part of a bearing sealing device.
2. Description of the Prior Art
The conventional rotation detecting device for use in association with an anti-skid brake system for minimizing the hazard of an automotive vehicle being skidded includes, in general, a serrated rotor and a detecting sensor, which are arranged spaced a distance from each other by means of a sealing device used to seal a bearing assembly, but are functionally integrated together to define a single and independent rotation detecting device.
This conventional rotation detecting device is of a structure in which the number of revolutions of the serrated rotor mounted on a rotary shaft for rotation together therewith can be detected by the revolution detecting sensor fitted to a knuckle. The bearing assembly incorporating such rotation detecting device is protected by the sealing device, disposed independently and laterally of the rotation detecting device, from an undesirable ingress of foreign matters such as dusts and dirt and/or water.
The Japanese Patent No. 2816783, for example, discloses a bearing seal assembly incorporating therein a rotation detecting device for detecting the number of revolutions of a vehicle wheel. To reduce the space for mounting of the rotation detecting device and to improve the detecting performance thereof, the bearing seal assembly having the rotation detecting device includes an annular slinger and an elastic member admixed with a powdery magnetic material and bonded by vulcanization to the annular slinger, with a plurality of opposite magnetic poles defined so as to alternate circumferentially of the elastic member. The slinger and the magnetized elastic member bonded to the slinger form a magnetic encoder.
The Japanese Laid-open Patent Publication No. 6-281018, for example, discloses a built-in coder sealing structure so designed as to reduce the axial dimension of the sealing structure, to increase the sealability between a rotating element and a stationary element and to render it to be easily mounted. According to this laid-open patent publication, a gap between the rotating element and the stationary element is sealed and a rotary disc is mounted on the rotating element for rotation together therewith. A coder magnetized to have a plurality of opposite magnetic poles is mounted on the rotary disc and built in the sealing structure. This coder is a magnetic encoder made of an elastomer added with a powdery magnetic material and is used as a sealing means in which a side face of the coder is held substantially level with a side face of the stationary element.
The magnetic encoder suggested in any one of the foregoing patent literature is of a structure in which the multi-pole magnet member is mounted on a core metal serving as a slinger which is in turn press-fitted onto a bearing inner race or the like. However, even though in the conventional magnetic encoder of the kind discussed above the firm mounting of the core metal onto the bearing inner race under the interference fit is achieved, there is a high possibility that when the use is made under extremely severe conditions, salty water or the like may enter the bearing assembly through an interface between the core metal and the bearing inner race and will therefore affect the lifetime of the bearing assembly adversely. Because of this, improvement of the sealing performance is demanded to avoid the problem. More specifically, even though the sealing device per se can exhibit a satisfactory sealing performance, the interface between the bearing inner race and the core metal of the magnetic encoder which is a component part of the sealing device is also required to be sealed when the core metal is mounted on the bearing inner race.
Also, if the fitting of the core metal of the magnetic encoder to the bearing inner race is too tight, in other words, the amount of interference fit is too large, a pressing force during the press-fitting of the core metal onto the bearing inner race becomes too large and, therefore, there is a high risk of the core metal being undesirably deformed. Once the core metal is so deformed, a gap is developed between the deformed portion of the core metal and the bearing inner race, causing reduction in sealability.
Although the above magnetic encoder uses a rubber magnet as the multi-pole magnet member, it may also use a multi-pole magnet member prepared from a sintered element in order to increase the sensitivity. In this case, cracking in the magnet member due to the press-fitting of the magnetic encoder onto the bearing inner race has to be taken into consideration.
In the conventional magnetic encoder employing the rubber magnet, the amount of the powdery magnetic material to be used in the rubber magnet cannot be increased and, therefore, increase of the detecting sensitivity is naturally limited. This is because, if the amount of the powdery magnetic material to be mixed is too large during the process of kneading the powdery magnetic material, not only is a kneading machine apt to be damaged considerably, but also the powdery magnetic material tends to be oxidized in contact with heat evolved during the processing with the magnetic characteristic consequently deteriorated. Also, with the magnetic encoder employing the rubber magnet, there is a high possibility that the surface of the magnetic encoder will be damaged or scratched in contact with sand particles or the like that are trapped in between the surface of the magnetic encoder and the magnetic sensor confronting with such magnetic encoder surface.
The same applicant as that of the present invention has therefore suggested a magnetic encoder including a multi-pole magnet member. This multi-pole magnet member is a sintered element prepared by sintering a mixture of a powdery magnetic material and a powdery non-magnetic material. See the Japanese Laid-open Patent Publication No.2004-037441. However, the magnetic encoder having the multi-pole magnet member prepared from the sintered element appears to be damaged by strong impacts.